In the manufacture of profiles which are at least in part closed (slotted profiles) or of such semi-finished products continuous or discontinuous forming methods may be used. Continuous forming is performed by roll forming, for example. Discontinuous methods are preferred when continuous roll forming cannot be applied on account of a complex profile or semi-finished product geometry. So-called U-O forming, for example, is known in the discontinuous manufacture of profiles or semi-finished products which are at least in part closed.
The prior art also includes the manufacture of three-dimensionally shaped components of sheet metal by way of the progressive die method (see, for example, US 2002/0162297 A1, FIGS. 6 to 8).
In the automotive industry, closed profiles from sheet metal are used as structural components, for example as bumpers and shock-absorbing hollow sections. Occasionally there is also demand for slotted or closed sheet-metal profiles which have undercuts, such as, for example, pleats, embossings, elevations, or similar shaped elements which run transversely to the longitudinal axis of a hollow section. In the case of a crash, such undercuts may serve to increase the rigidity of the component and/or to influence the behavior under deformation, for example.
Manufacturing subsidiary shaped elements, such as pleats or similar embossings, in longitudinal welded hollow profiles by means of a mandrel which is disposed in the hollow profile produced from a sheet metal blank is proposed in DE 10 2004 046 687 B3 (see para. [0032] therein). The mandrel in this case has an embossing installation for embossing the sheet metal which is wrapped around said mandrel. Such a mandrel may also have subsidiary structures for embossing which are not constant in terms of length, provided there is the possibility for the mandrel to be removed after forming, this being the case with a conical basic structure, for example. In order to be able to also configure shaped elements of comparatively large volumes in a reliable manner, the embossing installation for this purpose may be configured as an embossing die which is displaceable beyond the circumference of the mandrel, and shaping elements as counterparts to the shaping which is produced by the embossing installation may be provided in clearances of the die halves which enclose the mandrel.
However, the proposal disclosed in DE 10 2004 046 687 B3 is not, or is hardly suitable for manufacturing substantially cylindrical hollow profiles having undercuts, in particular inwardly oriented undercuts, since the described mandrel cannot, once the undercut has been embossed, be removed from the closed hollow profile again in such cases.